(NEXSTAR) — They’ve roamed through storybooks, movies and our imaginations, and now, scientists say Tyrannosaurus rexes were positively abundant when they still walked the earth. According to a new study published in the journal Science, approximately 2.5 billion T. rexes in total have lived on the planet.

The scientists estimate that there were about 20,000 T. rexes on Earth at any given time. The study’s data suggests that only 1 per 80 million T. rex skeletons have been recovered.

The researchers calculated the T. rex population over 127,000 generations by taking into account their body sizes, sexual maturation and their energy needs. The calculation framework can be applied to any taxon with the right data, the University of California, Berkeley scientists said.

“It also opens the door for other types of analysis,” the study says, such as determining the rarity, geographic restrictions and timespan of various species.